Brugada syndrome is a distinct form of genetically-determined idiopathic cardiac arrhythmia syndrome that can lead to syncope, cardiac arrest and sudden cardiac death (SCD). The syndrome is a genetic form of cardiac rhythm disorder caused by an inherited ion channelopathy. Brugada syndrome has been observed in the electrocardiograms of otherwise healthy young individuals without evidence of structural heart disease who are of Southeast Asian descent. Men are eight to ten times more likely to suffer Brugada syndrome. The syndrome has an autosomal-dominant pattern of transmission in about half of the familial cases observed and primarily affects Southeast Asian men, especially Thai and Laotian, in the 30-50 year age range, with a median age of 41 years.
The prognosis in Brugada syndrome is poor. Although the exact incidence of SCD due to Brugada syndrome is unknown, the magnitude of the problem has been estimated to range from 180,000 to 450,000 deaths annually in the United States alone. Further, about 2.5% of all cardiac arrest cases in which the patient showed no clinically identifiable cardiac abnormalities have been attributed to Brugada syndrome. The syndrome also accounts for 4% to 12% of all SCDs in genetically pre-disposed individuals, and a 40% mortality rate has been observed in symptomatic patients at two to three years follow up, with a 2% to 4% mortality rate in asymptomatic patients. During electrophysiologic studies (EPS), asymptomatic patients with induced ventricular tachycardia (VT) or ventricular fibrillation (VF) exhibited four times more SCD than non-inducible patients.
The cause of death in Brugada syndrome is due to VF, yet the precise mechanism underlying the electrocardiographic changes observed in symptomatic patients having Brugada syndrome is unknown. Pathologically, in 20% of observed cases, the syndrome has been associated with mutations in SCN5A gene expression, located in chromosome 3, which encodes for sodium ion channel transport to cell membranes of cardiac myocytes. Loss-of-function mutations in this gene have been theorized to lead to a failure of the action potential dome to develop, that in turn causes persistent ST segment elevation. The clinical events observed coincident to the electrocardiographic markers of Brugada syndrome, from syncope to VT to VF to SCD, are triggered by polymorphic ventricular arrhythmias, whose mechanism could be a Phase 2 reentry in the area around the right ventricular outflow tract.
Conventional approaches to treating Brugada syndrome focus on preventing or ameliorating VT and VF. For instance, implantable cardiac rhythm management devices, particularly automatic implantable cardioverter-defibrillator (ICDs), and, to a lesser extent, transiently-introduced electrophysiology catheters, apply a therapy based on the reversion of already-established polymorphic arrhythmias, such as described in Lee et al., “Prevention of Ventricular Fibrillation by Pacing in a Man with Brugada Syndrome,” J. Cardiovasc. Electrophysiol., Vol. 11, pp. 935-937 (August 2000), the disclosure of which is incorporated by reference. Similarly, Quinidine-based pharmaceutical therapies have also been used to effectively prevent VF induction and suppress spontaneous arrhythmias. Finally, surgical interventions through ablation at the right ventricular outflow tract level have been explored. Notwithstanding, these approaches constitute aggressive interventions and are impracticable to use on the large population that is theorized to have the Brugada syndrome, as only a small percentage will develop VT or VF, or experience cardiac arrest or SCD.
Therefore, a need remains for an approach to proactively treating the conduction and activation problems underlying the Brugada syndrome, rather than focusing on only avoiding or alleviating the deleterious sequalae of the syndrome.
A further need exists for an approach that can utilize commercially available cardiac arrhythmia devices for treating the conduction and activation problems underlying the Brugada syndrome.